1. Field of the Invention
The present invention relates to an anodic bonding method and a piezoelectric vibrator manufacturing method.
2. Description of the Related Art
In the related art, in the manufacturing process of piezoelectric vibrators or semiconductor components, anodic bonding has been performed to bond a silicon wafer or the like to the surface of an insulating material such as glass.
The anodic bonding is a method of bringing metal, silicon, or the like to be bonded into contact with one surface of an insulating material such as glass and bringing a cathode made of metal into contact with the other surface of the insulating material, thus bonding the metal and the insulating material together with the application of a DC voltage under a temperature condition of 300° C. to 400° C.
In such an anodic bonding method, the surfaces which face each other so as to bond the metal and the insulating material together have micro unevenness, warping, or the like. Therefore, the entire bonding surfaces are not closely adhered at the same time, but in many cases, between the metal and the insulating material, a bonding portion widens concentrically on the bonding surfaces from a plurality of contact points. Thus, there is a problem in that air is trapped in areas between a plurality of bonding portions, which remain unbonded all the way on the bonding surfaces, and voids are formed in the non-bonded areas.
As an anodic bonding method for suppressing such voids, JP-A-63-229853 discloses an anodic bonding method which uses an anodic bonding machine having a cathode electrode configured by a plurality of concentric annular electrodes to sequentially apply a voltage from a central annular electrode to a bonding surface. In this method, a bonding portion widens in a radial form from one point on the bonding surface. Therefore, no areas which are surrounded by the interfaces of the plurality of bonding portions as described above will be formed, and it is possible to force out gas generated during the anodic bonding from the bonding surfaces.
However, in the anodic bonding method disclosed in JP-A-63-229853, a DC voltage is first applied to the central annular electrode, and the DC voltage is sequentially applied to the outer annular electrodes. Therefore, the DC voltage application time is different between the central and outer sides of the insulating material being anodically bonded.
In this case, in the bonding portion at the central side of the insulating material, the voltage would be applied for an excessively long period even though it has been bonded completely. Moreover, in the area where the voltage is applied for an excessively long period, much gas will be generated during the anodic bonding. The gas generated at the interface of the metal and the insulating material after the anodic bonding will become the cause of defects of the anodic bonding like the voids.
Therefore, there is a problem in that the bonding surface between the metal and the insulating material anodically bonded by the anodic bonding method disclosed in JP-A-63-229853 exhibits uneven quality between the central and outer sides. This problem will be more noticeable when large-size substrates are anodically bonded.
In addition, when piezoelectric vibrators, semiconductor components, and the like were manufactured by anodically bonding a metal wafer and an insulator wafer in accordance with the anodic bonding method disclosed in JP-A-63-229853, there is a concern that the bonding surface quality becomes uneven between the central and outer sides of the bonding surface of the wafer, thus causing bonding defects in the piezoelectric vibrators, semiconductor components, and the like.